Solution to PS 8 #12
Only cells that have taken up the intact plasmids form colonies, because
untransformed cells are sensitive to tertracycline. There are two
classes of plasmids: intact pBR322 formed by ligation of the ends cut by
PstI, and a recombinant molecule formed by insertion of the PstI
restriction fragment into the vector. Cells containing the intact vector
are resistant to ampicillin, whereas thse containing the recombinant are
sensitive to ampicillin, since the PstI site is within the amp8
gene. These two types of cells can be ditinguished by transferring
part of the colonies to another petri dish with medium containing ampicillin.
Cells from the colonies that fail to grow in the presence of ampicillin
conatin the recombinant plasmid.
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